1. Field of the Invention
The invention relates to a self-propelled civil engineering machine, and in particular a slipform paver, and to a method of controlling a self-propelled civil engineering machine.
2. Description of the Prior Art
There are a variety of known types of self-propelled civil engineering machine. Such machines include for example known slipform pavers or road milling machines. A distinguishing feature of self-propelled civil engineering machines is that they have a working unit which is arranged on a chassis of the machine and which has work-doing means for producing structures on a piece of ground or for changing the piece of ground.
On known slipform pavers, the working unit comprises an arrangement for moulding flowable material, and in particular concrete, which will also be referred to below as a concrete mould. Structures of different configurations, such as crash barriers or traffic islands for example, can be produced with the concrete mould. A slipform paver is described in, for example, EP 1 103 659 B1.
The working unit of known road milling machines is a milling arrangement which has a milling drum fitted with milling tools with which material can be milled off the ground over a preset working width.
Known civil engineering machines also have a drive unit having driving means to enable translatory or rotational movements to be performed by the civil engineering machine on the ground, and a control and calculating unit to control the drive unit in such a way that the civil engineering machine performs the translatory and/or rotational movements on the ground.
To produce structures on the ground or to change the ground, an attempt is made in the case of self-propelled civil engineering machines to achieve largely automatic control of the civil engineering machine without the need for any interventions worth mentioning by the driver of the machine. When the civil engineering machine is being controlled automatically, the drive unit of the civil engineering machine is controlled in such a way that, starting from a preset starting point at which the civil engineering machine is in a preset position and at a preset orientation on the ground, a reference point on the civil engineering machine is moved for a preset distance or path of travel or at a preset spacing therefrom, i.e. along a line equidistant from the distance or path of travel, in order to produce a structure or to change the ground. The preset distance or path of travel is defined by straight lines and/or curves in this case.
A known method of controlling self-propelled civil engineering machines presupposes the use of a string line by which the desired distance or path of travel or a line equidistant from the desired distance or path of travel is preset. It is also known for self-propelled civil engineering machines to be controlled by the use of a global navigation satellite system (GNSS). A road milling machine whose drive unit is controlled by a string line is known for example from U.S. Pat. No. 4,041,623. U.S. Pat. No. 5,988,936 describes a slipform paver having a system for controlling the drive unit by the use of a string line. In the case of both these civil engineering machines, the spacing between a reference point on the civil engineering machine and the string line is determined by sensing members which detect the string line.
The slipform paver which is known from U.S. Pat. No. 5,988,936 has a sensing member which is at the front in the direction of operation and a sensing member which is at the rear in that direction and a central sensing member which is arranged between the front and rear sensing members. All the sensing members lie on a common axis which extends parallel to the longitudinal axis of the slipform paver. The sensing members define reference points on the civil engineering machine.
When the slipform paver is moving along a straight section of the desired distance or path of travel, both the sensing member which is at the front in the direction of operation and the sensing member which is at the rear in that direction are in use and the drive unit is thus controlled both as a function of the distance measured between the associated front reference point on the civil engineering machine and the string line and as a function of the distance measured between the associated rear reference point and the string line. The drive unit is so controlled in this case that the spacing from the string line is equal to a desired value. Control of this kind has proved satisfactory in practice.
When the slipform paver is moving along a curved section on the other hand, the control of the drive unit takes place as a function only of the spacing which is measured between the associated central reference point on the civil engineering machine and the string line. The front and rear sensing members are not active in this case.
At the transition from a straight section to a curved section or vice versa, a changeover is therefore needed between the various sensing members. At the entry into the curve, a changeover is made from the front and rear sensing members to the central sensing member and at the exit from the curve a changeover is made back from the central sensing member to the front and rear ones. A changeover to various different sensing members proves to be a disadvantage simply because the changeover means that the process is not a continuous one. It is also a disadvantage that, when travel through a curve is controlled by the central sensing member, the position of the sensing member depends on the radius of the curve.
If however the slipform paver is to change its direction of operation at the transition from a straight section to a curved section, then problems arise in practice when the drive unit is controlled in the known way where provision is made for a changeover from the front and rear sensing members to the central sensing member at the entry into the curve. What is a particular problem for the control system in this case is entry into tight curves, such for example as when concrete components in the form of traffic islands are being produced.
It has also been found that the transition from the straight section of the desired distance or path of travel to the curved section is a particular problem for the control of the civil engineering machine, because the position of the discontinuity is not precisely known. It is true that in practice the driver of the machine can specify that the entry into the curve is to start. However, the exact position of the discontinuity is difficult for the driver of the machine to estimate. The position of the discontinuity cannot be determined solely by monitoring the spacing between the front reference point and the string line, which increases at the entry into the curve, simply because the control system is intended to correct any difference between the reference point and the string line, i.e. to keep the spacing to zero. Even if the changeover should take place at exactly the right point in time, what results in practice will be an abrupt steering command because it is most unlikely that the central reference point will be at exactly the same spacing from the string line as the front and/or rear reference point at the time of the changeover.